Patent GB-1412001-A (GB)
Title: Electrode for potentiometric measurements
IPC: G01N27/30
Filed: 1972-10-02
Abstract: 1412001 Electro-chemical analysis RADIOMETER AS 2 Oct 1972 45292/72 Heading GIN Reference and ion-sensitive electrodes include a body of an electrically conductive material hydrophobized with a solid hydrophobizing material, an electro-chemically active redox system sensitive to ions in solution, and a humid solid water-soluble compound which is able to dissociate with liberation of an ionic specie to which the redox system is sensitive. Reference electrodes. A cylindrical inert tube is partially filled with graphite hydrophobized with P.T.F.E. and a redox system such as quinhydrone or thymoquinhydrone is disposed therein in graded concentration so that one end into which an electrode extends is devoid of the redox system. The other end in in contact with a circular disc of porous P.T.F.E. containing in the porosities thereof the humid, solid water-soluble compound such as a mixture of oxalic acid and sodium oxalate, the surface of the disc not in contact with the redox system being porous to the sample solution when the electrode is inserted therein. Alternatively calomel paste and potassium chloride may be used instead of the quinhydrone and the oxalic acid mixture. A unified structure may be used. In a modification Fig. 3 (not shown) a further disc may be positioned in juxtaposition to the first disc made of solid hydrophobizing material which may contain in the porosities thereof the same solid water-soluble compound or a different one which serves as a salt bridge between the sample and porous P.T.F.E. disc. A still further disc may be added Fig. 4 (not shown) of P.T.F.E. permitting electrolytic communication between the sample and the salt bridge. In Fig. 5 the electrode body 16 contains a calomel paste redox system and is in contact with a humid powder mass of potassium chloride. The bottom of the electrode is provided with a porous glass or insulating material plug 24 or a non-porous plug the junction between the potassium chloride and sample being established as a sleeve type junction between cap 22 and plug 24. lon selective electrodes Fig. 6. The electrode body 16 of e.g. graphite hydrophobized with P.T.F.E. and including a mercury/calomel redox system and humid water soluble Ca Cl 2  layer 18 are positioned in inert tube 15 closed at one end by ion specific membrane 26 containing for example a solution of the calcium salt of di-(2- ethylhexyl)-phosphoric acid or di-(n-decyl)- phosphoric acid, sensitive to CA<SP>++</SP> ions. Other combinations are mercury/mercury oxalate as the redox system and calcium oxalate as the humid solid water-soluble compound. Both the redox system and water-soluble compound may be in layer 18. Flow through pH sensitive electrodes In these electrodes an annular region of electrode body 16 forms part of a tube through which the sample flows. A reference electrode may be provided at the end of the tube, Figs 7, 7a (not shown). Fig. 6 shows a cylindrical flow through reference electrode adapted to be arranged at one end of a flow through type electrode or electrode series. A cylindrical body 18 of porous hydrophobizing material contains the humid solid watersoluble compound in contact with the redox system of body 16.